Cell division, or mitosis, is the process which allows cells to multiply in order to repair or regenerate tissues and replace dead cells. In cancer cells, regulation of this process is defective and this is why these cells divide anarchically and give rise to tumours. Thus, one effective therapeutic route to prevent the development of cancer consists in blocking the division of cancerous cells using molecules with anti-mitotic properties.
In addition, every tumor needs nutrients and oxygen in order to grow. These elements are provided by intratumoral blood vessels which result from a mechanism known as angiogenesis. In fact, if these vessels are absent, tumour cells undergo a cell necrosis process, and tumour growth slows down then stops. An example of another therapeutic route to combat cancer therefore consists in blocking the angiogenesis process by blocking the molecules controlling this mechanism.
It would therefore be extremely useful to have available new anti-cancer molecules capable of inhibiting both tumour cell proliferation and the angiogenesis process in the tumour.
Moreover, the majority of current anti-cancer agents are not truly specific to tumour cells and therefore also target healthy cells, thus giving rise to many, and at times serious, side effects.
Still another problem linked to conventional anti-cancer drugs, such as paclitaxel, is that these molecules are often highly hydrophobic which makes it necessary to develop complicated and expensive pharmaceutical formulations in order to achieve acceptable bio availability in vivo. The problem of in vivo bioavailability is all the more acute in the case of treatment using nucleic acids since it is extremely difficult for them to reach their target cells in an efficacious and specific manner.
It would therefore be extremely useful to have available new anti-cancer molecules which present the following characteristics:                much improved efficacy as a result of their dual inhibitory action on tumour proliferation and angiogenesis such that they can be effective alone, without the use of conventional chemotherapy or radiotherapy and thus greatly the limit side effects linked to these types of treatment,        a fairly broad spectrum of activity against angiogenic factors to prevent resistance to treatment,        very few side effects as a result of greater specificity towards tumour cells,        a synthesis process that is easily adaptable to an industrial scale,        easier to use, notably as a result of better bioavailability and/or longer half-life in vivo, in particular as a result of direct specificity for tumour cells, with good solubility in aqueous media and improved resistance to in vivo breakdown processes.        
WO2007/125210 (1), the whole content of which is herein incorporated by reference, discloses promising compounds useful notably for cancer treatment.
These compounds display several advantageous properties:                they are capable of having high anti-tumour efficacy alone as a result of a dual effect on tumour proliferation and angiogenesis, efficacy that makes it possible to envisage a single treatment without being combined with a conventional chemotherapy molecule such as taxol;        they do not have specificity for a particular type of cancer but rather a broad spectrum of activity against tumour cells and activated endothelial cells;        they have very few side effects in vivo as a result of specificity for tumour cells and activated endothelial cells compared to healthy cells;        they have a synthesis process that can be easily adapted to an industrial scale; and        they have sufficient bioavailability in vivo in order not to require the development of particular pharmaceutical forms.        
These compounds are thus very interesting since they combine many advantages necessary for the development of a new, simpler, cheaper and efficient anticancer treatment. They were also found to be good candidates for the development of new, simpler, cheaper and efficient anti-inflammatory agents.
However, it is always necessary to improve the antitumor efficiency of existing compounds. It would thus be very useful to find optimized compounds with a higher efficiency but keeping all the other advantages of these promising compounds.
The compounds of WO2007/125210 are new pseudopeptide compounds consisting of a support to which at least three pseudopeptide units are coupled. Such compounds bind surface nucleolin and display anticancer (anti-angiogenic and anti-mitotic) and anti-inflammatory activities.
It is believed that these compounds act by the interaction of the at least 3 pseudopeptide units grafted on the support with the RGG domain of surface nucleolin.
Preferred compounds have a peptide support, in particular a linear peptide support with a helicoidal structure, to which at least 3 [Lys-Ψ-Pro-Arg] (also named KΨPR) units are coupled.
In this document, a conventional method was used for preparing the KΨPR units, as described in US20040002457A1 (2) and Nisole et al (3). In such a conventional method Proline derivative which contains a secondary amine reacts with the Boc-Lys(Boc)-CHO (aldehyde) to form an enamine with partial loss of chirality at the Lys residue (5-10%). Thus, at the end of such a conventional reaction, the reaction mixture comprises 90-95% L-Lys-Ψ-Pro-Arg units and 5-10% D-Lys-Ψ-Pro-Arg units.
As a result, when this mixture is used for coupling onto the ε amino groups of the lateral chain of the Lys residues of the support peptide, a mixture of stereoisomers is obtained. Since each Lys-Ψ-Pro-Arg unit may have either a L or D lysine, the number of stereoisomers that are obtained increases exponentially with the number of KΨPR units. For preferred compounds with 5 or 6 units, the number of obtainable stereoisomers is 32 and 64 respectively.
Similarly, performing the reductive amination step directly on-resin by reaction with Boc-Lys(Boc)-CHO with the secondary amines of pro line residues grafted on a solid support in the presence of an hydride reagent also results in the production of a mixture of stereisomers.
Using this conventional method, the obtained pseudopeptide compound is not optically pure but in contrast is composed of a very complex mixture of stereoisomers, which cannot be isolated or purified due to the mixture complexity. Indeed, the mixture is composed of a too high number of very close stereoisomers, which cannot thus be each isolated by usual purification technologies. Individual steroisomers of the compounds of interest cannot thus be purified from the complex mixture obtained using the conventional method for preparing these compounds.
The inventors have used a new method for preparing the KΨP dipeptide, which permits to obtain an optically pure L-Lys-Ψ-Pro or D-Lys-Ψ-Pro compound. This method has been adapted from the article by Cushman et al (4), which described an epimerisation effect when preparing Phe-Ψ-Pro dipeptides using the conventional method and a new method for the preparation of pure L-Phe-Ψ-Pro dipeptides.
The inventors then prepared optically pure compounds consisting of a linear support peptide to which at least 3 L-Lys-Ψ-Pro-Arg or D-Lys-Ψ-Pro-Arg units are coupled. In such optically pure compounds, the lysine residues of the various Lys-Ψ-Pro-Arg units are either all in L configuration or all in D configuration.
Surprisingly, they found that these optically pure compounds display a significantly higher anticancer efficiency than a composition comprising a mixture of stereoisomers of the same compounds.